The origin, function and fate of germinal center cells in peripheral lymphoid tissue will be examined. Transfers of labeled cells such as spleen and bursa in histocompatible chickens, immune lymph node in rabbits and bone marrow in inbred mice will be employed. Particular attention will be given to the possible influence of specific antigen and antigen-antibody complexes on the homing of lymphoid cells. The memory function of thymus and bone-marrow-derived lymphocytes (T and B cells) and the cell interactions during the secondary immune response in vitro will be analyzed. Reconstitution of the immune responsiveness of mouse or chicken cells, which have been rendered incompetent after treatment with antisera and C (specific anti-thymus or anti-bursa, chickens; anti-O and anti-Ig, mouse), by addition of variety of immune and normal cells will be studied. Three experimental models will be used to obtain further information on the nature of the antigen-specific receptor of immune T cells. In one, the agammaglobulinemic, bursectomized chicken, in vivo inhibition of the delayed hypersensitivity resonse by anti-Ig sera, labeling of cell surfaces by I125, ad proliferative responses of spleen cells will be studied. In the second, the proliferative response of immune mouse lymph node cells, and in the third, the mixed lymphocyte reaction between rabbit thymus cells of different specificities, including anti-allotypes and anti-idiotypes, will be tested. BIBLIOGRAPHIC REFERENCES: Palladino, M.A., Lerman, S.P., and Thorbecke, G.J. Transfer of hypogammaglobulinemia in two inbred chicken strains by spleen cells from bursectomized donors. J. Immunol. 116:1673, 1976. Grebenau, M.D., Lerman, S.P., Palladino, M.A., and Thorbecke, G.J. Suppression of adoptive antibody responses by addition of spleen cells from agammaglobulinemic chickens "immunised" with histocompatible bursa cells. Nature 260:46, 1976.